The handheld glucose meters are intended for monitoring of patients with diabetes mellitus at home or other extra-laboratory settings. The recommended method for most meters currently in use is to apply a small drop of fresh capillary whole blood directly to the glucose test strip. The measurement is based on glucose oxidase reaction that consumes stoichiometric amount of molecular oxygen. Because of the ease of use and rapid turnaround time many hospitals use glucose meters for point-of-care testing (POCT) of critically ill patients. However, very low and high hematocrit and oxygen tension that may be present in samples of these patient have been reported to cause inaccuracy of the method. We investigated the effects of different hematocrit and oxygen tensions on the glucose measurements with the latest generation of test strips (Lifescan SureStepPro, Johnson & Johnson Company) that are used for POCT of critically ill patients in the Clinical Center. Heparinized venous whole blood was prepared to contain hematocrit between 10 and 68% (reference range: 32 ? 48%), glucose concentrations between 22 and 495 mg/dL, and oxygen tension between 30 and 245 mm Hg. The samples were analyzed simultaneously with SureStepPro tests strip (glucose) and with ABL 725 Clinical System (oxygen tension and glucose). The test strip glucose results, expressed as the difference (%) from the ABL results were not affected by the oxygen tension in the sample (p>0.2). The agreement between the test strip and ABL results was acceptable for samples with normal hematocrit (slope=1.04, intercept ?1.3). However, at hematocrit <32% the test strip overestimated the glucose concentration (slope=1.18, intercept=2.6). For samples with glucose concentration above 100 mg/dL and hematocrit <20% the overestimation was statistically (p<0.007) and clinically (up to 40%) significant. Based on these results the SureStepPro test strip can be used to measure venous whole blood glucose but should not be used for patients with extremely low hematocrit.